1 1 10 Appendix VL
rotations of A. Find the rotations and direction of motion of the arm
to cause them. (Hons. Applied Mechs. Exam,)
Referring to Fig. 974 and to p. 522.
If A be fixed and the arm rotates +
C's turns = H — for one rotation of arm
and C's turns = x (* + -) f°r x rotations of arm.
While these take place, imagine A to make y rotations, either -f
or — , let us say minus.
Total turns of C =
Then by Case (i)
/. x = -1-8
And the arm must turn through r8 x 360 = £50° in the same direction
as the rotations of A and C.
Again, By Case (2) : taking A's turns minus,
3 - *+i*+^
/. x = 1-4
or the arm must turn through 1*4x360 = 504° in the same direction
as C's rotations, but opposed to those of A.
P. jjo. Lapping of Belts.
Example 79. A rope has its direction changed through two right
angles by passing round a grooved guide pulley whose diameter is
12 ins. ; the diameter of the axle being ij ins., and \i for axle = "07.
How is the efficiency of the pulley affected by axle friction when a
load of 2500 Ibs. is being raised ? If the- pulley were fixed so that it
could not turn, how would the efficiency be affected by the friction of
the rope on the pulley when ^ = *6 ? (Hons. Applied Mechs. Exam.)
Case i. P = 2500
P1= 2500+ (P1 + 25oo)x *07X~ = 2536
Efficiency = = -98
* 2536 -^-